Organic Chemistry In The First Phases Of Solar-type Protostars

By Keith Cowing
June 29, 2022
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Organic Chemistry In The First Phases Of Solar-type Protostars
Sketch of the two major paths invoked in the literature for the formation of iCOMs. Both predict that, during the cold molecular cloud/prestellar core stages (§ 3), the interstellar grains are covered by icy mantles whose constituents are the result of the hydrogenation of atoms and simple molecules, such as CO, and the oxidation of CO into CO2 (§ 2.2). After this first step, the two paths differ as follows. Left panel: In the Gas + grain chemistry path, the mantle components are either partially or completely injected into the gas-phase by thermal and non-thermal desorption processes (§ 2.3), where they undergo gas-phase reactions, which convert them into iCOMs (§ 2.4). This path can occur either in cold regions (i.e. in prestellar cores (§ 3), outer protoplanetary disks (§ 5) and molecular outflows (§ 6)) via non-thermal desorption (§ 2.3.2) of the mantles or in warm regions (i.e. in hot corinos (§ 4) and inner protoplanetary disks (§ 5)) via thermal sublimation (§ 2.3.1) of the mantles. Right panel: In the Only grain chemistry path, there are two major pathways: diffusive and non-diffusive iCOM formation (§ 2.5) and iCOM formation via reactions involving ice water molecules (§ 2.6). In the first path, the icy mantles are processed by UV (photolysis) and CR (radiolysis) irradiation while being formed (§ 2.5.2). In the diffusive path, When the dust temperature increases, radicals on the mantles become mobile and diffuse (§ 2.5.3). When radicals meet on the grain surfaces, they combine forming iCOMs (§ 2.5.4). Some radicals are also predicted to meet and react in non-diffusive processes during the cold phase. In the second path, radicals landing onto the grain surfaces from the gas-phase react with water molecules of the ice, forming iCOMs (§ 2.6).

Planetary systems such as our own are formed after a long process where matter condenses from diffuse clouds to stars, planets, asteroids, comets and residual dust, undergoing dramatic changes in physical and chemical state in less than a few million years.

Several studies have shown that the chemical composition during the early formation of a Solar-type planetary system is a powerful diagnostic to track the history of the system itself. Among the approximately 270 molecules so far detected in the ISM, the so-called interstellar complex organic molecules (iCOMs) are of particular interest both because of their evolutionary diagnostic power and because they might be potential precursors of biomolecules, which are at the basis of terrestrial life.

This Chapter focuses on the evolution of organic molecules during the early stages of a Solar-type planetary system, represented by the prestellar, Class 0/I and protoplanetary disk phases, and compares them with what is observed presently in Solar System comets. Our twofold goal is to review the processes at the base of organic chemistry during Solar-type star formation and, in addition, to possibly provide constraints on the early history of our own planetary system.

C. Ceccarelli, C. Codella, N. Balucani, D. Bockelée-Morvan, E. Herbst, C. Vastel, P. Caselli, C. Favre, B. Lefloch, K. Öberg

Comments: Chapter for Protostars & Planets VII
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2206.13270 [astro-ph.SR] (or arXiv:2206.13270v1 [astro-ph.SR] for this version)
Submission history
From: Claudio Codella
[v1] Mon, 27 Jun 2022 13:04:47 UTC (11,666 KB)
Astrobiology. Astrochemistry,

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